function [ ] = mx_eyecmd_printf( )
%MX_EYECMD_PRINTF The EyeLink tracker accepts text commands through the link.
% These commands may be used to configure the system, open data files, and so on.
%
% Remarks:
% The function waits up to 500 msec. for a success or failure code to be returned from the tracker, then returns the error code NO_REPLY. If you need more time, use eyelink_timed_command() instead.
% Parameters:
% fmt 	Similar to printf(), format string plus arguments.
% Returns:
% 0 if successfully executed, else error code.
%
%----------------------------------------------------------------------------
% Copyright Eduardo Aponte 2013
% aponteeduardo@gmail.com